The present disclosure pertains to a new apparatus and method for partial pre-reduction of iron or ferro-alloy ores, using fine particulate ores and fuel gas or coal-based producer gas in a hot cyclone reactor. The producer gas is preferably derived from the off gas resulting from operation of a bath smelting process. The melted and partially reduced iron that exits the hot cyclone reactor can then be gravity-coupled to a bath smelting process for complete reduction of ore to liquid iron or steel.
The disclosed apparatus and process obviates the need for indurated iron or ferro-alloy ore pellets. It also eliminates the need for coking of the coal used in the disclosed processes.
Both environmental and economic considerations have led to renewed efforts to develop effective iron smelting processes and equipment utilizing coal, rather than coke. Among the current coal-based systems under consideration are bath smelting processes. The background of bath smelting processes and their perceived shortcomings are described in a paper titled "Flash Melting and Partial Reduction of Iron Ore Concentrates" by Robert W. Bartlett, published in Salt Lake City, Utah in 1988 at the Center for Pyrometallurgy Symposium. That paper is hereby incorporated into this application by reference.
The referenced paper describes efforts to evaluate improvements in bath smelting processes for iron ores by flash melting particulate ores as they are descending to the bath. To do this, the ore particles are injected with a carrier gas and allowed to react with the bath off-gases as they rise between the bath and injector.
Partial reduction of iron oxide particles is initiated as the ore particles are delivered to the bath. This occurs in a quasi-counter current system in which the rising reducing gases flow by the descending ore particles. The difficulties perceived in this system revolved about the very short free flight residence time of the particles, which particularly limited pre-smelting reduction of larger ore particles.
The principle of cyclone firing entered practical boiler construction in the nineteen forties. The appeal of the cyclone configuration is that it gives flash combustion efficiency through turbulence enhanced mass and heat transfer and reaction rates. Pyrometallurgical processes using cyclones were first suggested in the mid-1950's, when a plant was built in Sardina to treat antimony concentrates. Another early use was developed in the USSR for copper concentrates.
As mentioned in the referenced paper, high temperature entrained flow smelting (e.g. cyclone smelting) has been suggested as an alternative to bath smelting to use pulverized coal and dry iron ore concentrate. The application of cyclones to iron ore reduction was first attempted in 1955. The research was not successful and was terminated in 1966.
The ability to produce iron through the use of fine particulate ores and coal as starting materials is significant due to: the phase-out of coke ovens and the environmental costs associated with coking, the need for a coal-based iron process, the existence of a large amounts of fine taconite, and the fact that a process based upon treating fine particles would be more economic because pelletizing and pellet induration would not be required.
The presently-described use of a cyclone reactor to partially reduce iron ore fines pores a number of advantages, for example: utilization of waste producer gas from the primary smelting furnace, high throughout being possible in a small reactor, enhanced heat and mass transfer rates, increased mixing of particles and gases due to high turbulence, use of high reaction temperatures, rapid reaction times available when dealing with small particles, elimination of induration, the use of coal in place of coke, and rapid separation of liquids and gases.